Rubber vulcanization with substituted tetramethylene thiurams and dithiocarbamates



in the vulcanization of raw rubber.

RUBBER VULCANIZATION WITH SUBSTITUTED TETRAMETHYLENE THIURAMS ANDDITHIO- CARBAMATES Frank A. V. Sullivan, Glenbrook, Conn., assignor toAmerican Cyanamid Company, New York, N.Y., a corporation of Maine NoDrawing. Application January 9, 1956 Serial No. 557,839

Claims. (Cl. 260-795) the process of this invention are thiuramdisulfides and the zinc salts thereof having the formula wherein R isselected from the group consisting of H i and CH3.

The accelerators of the present invention are useful with natural rubberas well as synthetic rubber. By the latter is meant synthetic likepolymers of butadiene-1,3

and copolymers of butadiene-1,3 with vinyl-type monomers copolymerizablewith butadiene-1,3 such as acrylonitrile, styrene, acrylamide and thelike. Because of their ultra accelerating activity, the accelerators ofthis invention, particularly the dithiocarbamates, find use in thevulcanization of natural and synthetic latices as well as In addition,they may be successfully used as activators with other types ofaccelerators, e.g., the thiazoles.

The amount of accelerator employed may vary according to the particularcomposition being treated. In the case of the disulfides it may alsovary depending on whether or not free sulfur is present. When used innatural rubber or latex, the accelerator may be present in amounts ashigh as 5% on the rubber. Usually, however, it will not be more thanabout 3 or 4%. When treating synthetic rubber-like polymers andcopolymers or synthetic latices, the amount of accelerator willgenerally be somewhat less. In either case, the amount of acceleratorwill usually not exceed 1.5%, being for the most part employed inamounts of about 0.2-1.0%.

The thiuram disulfides of this invention may be prepared by oxidizing anaqueous solution of a salt of the corresponding alkyl substitutedcyclotetramethylene dithiocarbamic acid. The corresponding zinc salt ofthe thiuram disulfide may be prepared by reacting the dithio carbamicacid with a zinc salt.

The following examples further illustrate the invention.

All parts are by weight unless otherwise indicated.

Hal-C g 5 CH: H:

2,879,262 Patented Mar. 24,. 1959 28.6 parts of sodium2-methyltetramethylene dithiocarbamate are dissolved in 150 parts ofwater. To this is added dropwise at 2535 C. a mixture of 9.3 parts ofglacial acetic acid and 2.65 parts of a 30% solution of hydrogenperoxide. On completion of addition the reaction mixture is digested for0.5 hour and then filtered. The product is washed, dried andrecrystallized to give a 64% yield of product melting at 128-131 C.Percent nitrogen-theory 8.75; found 8.71.

EXAMPLE 2 Zinc N,N'-2-methyltetramethylene dithiocarbama te on. on,

HrC-CH H-CH:

To parts of a 70.7% aqueous solution of Z-methylpyrrolidine dissolved in250 parts water containing 40 parts of NaOH is added 76 parts of carbondisulfide at 40-42 C. On cooling to room temperature, sodiumZ-methyltetramethylene dithiocarbamate precipitates ne cessitating, theaddition of. an additional 250 partsof water to keep it in solution. Tothis solution is added 91.7 parts of zinc acetate dissolved in 300 partsof water and the reaction mass stirred for four hours. The precipitatewas then separated by filtration, washed in water and dried at 105 C.The yield of crude product approaches quantitative and onrecrystallization from butyl cellosolve melts at 187-188 C. Percentnitrogentheory 7.26; found 7.02. Percent sulfur-theory 33.2; found 33.0.

ice

EXAMPLE 3 N,N-2,5-dimethyltetramethylene thiuram disulfide CH5 CH3 13.8parts of sodium N,N-2,S-dimethyltetramethylene dithiocarbarnate aredissolved in parts of water. To this solution is added dropwise at '5l0C. a mixture of 3.2 parts of a 30% solution of hydrogen peroxide and 6.8parts of concentrated hydrochloric acid and 35 parts of water. Oncompletion of addition the reaction mix ture is digested an additional0.5 hour and filtered. The product is washed and dried to give an 86%yield of product melting at-144l48 C.

EXAMPLE 4 Zinc N,N-2,5-dimethyltetramethylene dithiocarbamate CH; CH;

HaC- H HCH:

11.7 parts of sodium N,N-2,S-dimethyltetramethylene dithiocarbamate isdissolved in 20 parts of water. This solution is added simultaneouslywith a solution containing 3.4 parts of zinc chloride in 20 parts ofwater to a flask containing 20 parts of water. After addition iscomplete, the reaction mixture is stirred at 90 C. for 0.5 hour. Theproduct is separated by filtration, washed and dried to give aquantitative yield of product melting at 243-245 C. v

The following examples demonstrate the vulcanization of dry rubber andlatex using the accelerators of this in- 3 i rt. vention. Unlessotherwise noted, all parts are by weight. TABLE III Modulus and tensilestrength are measured in p.s.i.

EXAMPLE 5 15 Min. Cure 20 Min. Cure Compositions are prepared accordingto the following 5 Compound Mod., Per- Mod., base formula: 300% Tens.cent 300% Tens. cent Elong. Elong. Compound: Parts Smoked Sheets m ziiitig 350 2 750 700 350 2 700 110 uram u e. Zmc 9. N,N-2,5-dln1ethylSteanc acid 1 tetramethylene Whiting 30 thiuram dlsulfide. 250 2,175 750300 2,725 730 Sulfur 2 Light process oil 2 EXAMPLE '8 AcceleratorExample 6 is repeated except that the zinc salt of Samples of thesecompositions are then cured at 130 C. N,N"2,5-dimethyltetfamethylenedithiocafbamate is for 15 and minute periods. Results appearin Table I.P y 1H l l 0f the Z1110 Salt of Y TABLE I methylene dlthlocarbamate andmodulus 18 at 300% Resuits similar to those of Example 6 are obtained asshown 20 in Table IV. 15 Min. Cure 20 Min. Cure TABLE IV Compound M d '1P t M d '1 P t 0 EDS. cream 0 811$. GI'CBD 50 long. 5 0% 1 5 M311. Cure10 Mill. Cure Compound M d P M d P Tetramethyl 0 er- 0 erthiuramdlsulfide- 1, 325 3, 050 000 1, 200 2,826 680 20 300% Tenscent 309% Tenscent N,N-2-rnethyl Elena. g-

tetramethylene thluram disulfide- 1,200 2,375 .00 1,250 2,850 080 Znmethyltetra- The results of Table indicate that the thiuram digfiggglg'ggglg 250 2,500 800 275 2,800 770 sulfide accelerator of thisinvention 1s about as fast as Z ty 1 375 7 95 tetramethyl thiuramdisulfide, one of the better comfi igfigg flf 0 mercially availableultra accelerators, and is substantially th 0 0 2.700 780 300 2,975 770equivalent in other respects.

EXAMPLE 6 The following example illustrates the use of an accelerator ofthis invention in latex. The procedure of Example 5 is repeated exceptthat the accelerators were changed and the compositions tested EXAMPLE 95 -232 5? tunes of 5 and 10 mmutes' Results appear m Compositions areprepared according to the following TABLE H 40 base formula:

Compound: Parts 5Min. Cure 10 Min. Cure Rubber from latex :100 compoundZinc oxide 2 ,Mod., Tens. Percent Mod., Tens. Percent Sulfur L5 Elollg-Elflngt Titanium dioxide s Antioxidant 1.5 ZnN N'-2-.1neth ltetrhmethyleng Casein 1 .dithiooarbamete 975 2,900 '750 975 2, 950 740Surface agave agent 1 Zn (dibutyl dl- A 1 t 1 thlccarbamate).-- 650 1,825- 140 see are) 730 We Zn (diethyl dlihiowbamatehn 875 2.750 1.000 2,975 760 Samples of the compositions are then cured for 7% and 10 minutesat C. Results appear in Table V.

TABLE V 7% Min. Cure at 100 0. 10 Mm. Cure at 100 0.

Compound Mod, Mod, Per- Mod., Mod, Per- 500% 700% Tens. cent 500% 700%Tens. cent Elong. Elong.

Zn N,N-?fn1ethyltetramethylene ditbiocarhamate 375 1, 550 5,100 930 3751, 700 4,025 ,900 Zn (diethyl dithlocarbamate) 325 1,250 4, 825 980 4251, 800 4, 950 S90 Zn (dibutyldithlocarbamate) 475 2,275 4,575 830 1,0504,050 860 The results show that the accelerator according to this Iclaim:

invention is faster than either zinc (dibutyl-) or zinc (diethyldithiocarbamate) both excellent, commercially available accelerators.

EXAMPLE 7 The procedure of Example 5 is again repeated except thatN,N'-2,4-di1nethyltetramethylene thiuram disulfide is substituted forthe Z-methyl derivative and modulus is at 300%. Table III.

Similar results are obtained as shown in 2,879,262 5 pound isN,N'-2-methyltetramethy1ene thiuram disulfide. pound is zincN,N'-2,S-dimethyltetramethylene dithiocar- 3. A method according toclaim 1 in which the combamate. pound is zincN,N'-2-mcthyltetramethylene dithiocarbam- References Cited in the file fthis patent UNITED STATES PATENTS 4. A method according to claim -1 inwhich the com- 5 pound is N,N'-2,S-dimethyltetramethylene thiuram disul-1,445,621 Cadwell Feb. 20, 1923 fide. 2,283,334 Neal May 19, 1942 5. Amethod according to claim 1 in which the com- 2,665,268 Butler Jan. 5,1954

1. A METHOD OF VULCANIZING AN UNVULCANIZED ELASTOMER SELECTED FROM THEGROUP CONSISTING OF NATURAL RUBBER AND SYNTHETIC RUBBER-LIKEBUTADIENE-1,3 POLYMERS WHICH COMPRISES INCORPORATING IN SAID ELASTOMEROF A COMPOUND SELECTED FROM THE GROUP CONSISTING OFN,N''-2-METHYLTETRAMETHYLENE THIURAM DISULFIDE,N,N''-2,5-DIMETHYLTETRAMETHYLENE THIURAM DISULFIDE AND THE ZINC SALTSTHEREOF AND SUBJECTING THE RESULTANT MIXTURE TO HEAT FOR SUFFICIENT TIMETO ESTABLISH THE CURE.